NewAntFeaturesInDetail/PresetDef

If you want a version of <ant> with the logical default of inheritall="false", here it is

  <presetdef name="better-ant">
    <ant inheritall="false"/>
  </presetdef>

wherever you use <better-ant>, it will behave exactly like the <ant> task but with a different default value.

You can also define child elements. Say you want all your <javac> tasks to compile against a set of jars living in /our/jar/repository/, you could define

  <presetdef name="my-javac">
    <javac>
      <classpath>
        <fileset dir="/our/jar/repository/" includes="*.jar"/>
      </classpath>
    </javac>
  </presetdef>

and use <my-javac> wherever you'd use <javac> instead.

It is interesting to note that both <presetdef> and <macrodef> dynamically define a task that can then be invoked as any other. Properly declared, the resulting tasks can be used interchangeably. Here is a simple example, in which the filter target will echo a message either to the console or to a file depending on whether the property destfile has been set:

  <target name="-tocon" unless="destfile">  
    <macrodef name="myecho">
      <attribute name="message" />
      <sequential>
        <echo taskname="myecho"
              message="Echoing a message to the console:" />
        <echo taskname="myecho" message="@{message}" />
      </sequential>
    </macrodef>
  </target>
  
  <target name="-tofile" if="destfile">
    <presetdef name="myecho">
      <echo file="${destfile}" />
    </presetdef>
  </target>
  
  <target name="filter" depends="-tocon,-tofile">
  
    <loadfile srcFile="${srcfile}" property="message">
      <filterchain refid="myfilter" />
    </loadfile>
    
    <myecho message="${message}" />
  </target>

Another current use for <presetdef> is to provide a work-around for a bug with the JDK 1.5beta1 javac compiler. The compiler accepts target="1.1" but for some reason this does not work unless one sets source="1.3" as well. As this is a temporary issue one does not want to modify the build script much. This can be achieved as follows:

  <available property="jdk1.5+" classname="java.util.concurrent.Callable"/>

  <target name="check-1.5" if="jdk1.5+">
    <presetdef name="javac">
      <javac source="1.3"/>
    </presetdef>
  </target>

  <target name="init" depends="check-1.5">
   ....
  </target>

This will make a new javac task which will call the current javac task with the source option set to 1.3. It will also whine that one is overwritting the javac task.